Small Engines (Lawn Mowers, etc.): Tecumseh 8.0 TVM220, blown engine, riding mower

Question
I just replaced a blown engine on my riding mower with a Tec 8hp model TVM220. Might have 4-5 hours on it. After running 15-20 mins.(engine hot) starts surging and within 10 secs just quits. Let cool for 5 mins starts again and same thing in another 10 mins or so. Dealer suggested coil so I replaced that...no help.  What to try next?

Answer
this sounds stupid but is all the safety switches hooked up I changed a motor one time that did this back fired and all kinds of stuff it was the switch under the seat but not saying this is your problem if it isn't the switches you might have to reset the valves check clearance let me know